1. Field of the Present Invention
The present invention relates to a laminated electronic component and a method for manufacturing the laminated electronic component, and more particularly, to a laminated electronic component with external terminal electrodes formed directly by plating so as to be electrically connected to a plurality of internal conductors, and to a method for manufacturing the laminated electronic component.
2. Description of the Related Art
As shown in FIG. 3, a laminated electronic component 101 typified by a laminated ceramic capacitor generally includes a component main body 105 having a laminated structure, which includes a plurality of laminated insulator layers 102 composed of, for example, a dielectric ceramic, and a plurality of layered internal electrodes 103 and 104 provided along interfaces between the adjacent insulator layers 102. Respective ends of the plurality of internal electrodes 103 and respective ends of the plurality of internal electrodes 104 are exposed at one end surface and the other end surfaces 106 and 107 of the component main body 105, and external terminal electrodes 108 and 109 are respectively arranged so as to electrically connect the respective ends of the internal electrodes 103 to each other and the respective ends of the internal electrodes 104 to each other.
For the formation of the external terminal electrodes 108 and 109, in general, a metal paste containing a metal component and a glass component is applied onto the end surfaces 106 and 107 of the component main body 105, and then baked, thereby forming paste electrode layers 110. Next, first plating layers 111 primarily including, for example, nickel are formed on the paste electrode layers 110, respectively, and second plating layers 112 primarily including, for example, tin or gold are further formed thereon. Thus, each of the external terminal electrodes 108 and 109 is formed in a three-layer structure including the paste electrode layer 110, the first plating layer 111, and the second plating layer 112.
The external terminal electrodes 108 and 109 are required to have excellent solderability when the laminated electronic component 101 is mounted on a substrate via solder. At the same time, the external terminal electrode 108 is required to electrically connect the plurality of internal electrodes 103 which are electrically insulated from each other, and the external terminal electrode 109 is required to electrically connect the plurality of internal electrodes 104 which are electrically insulated from each other. The second plating layers 112 described above ensure the solderability, whereas the paste electrode layers 110 electrically connect the internal electrodes 103 to each other and the internal electrodes 104 to each other. The first plating layers 111 prevent solder erosion in the solder joint.
However, the paste electrode layer 110 has a relatively large thickness from several tens of μm to several hundreds of μm. Therefore, in order to limit the dimensions of the laminated electronic component 101 within certain specifications, there is a need to reduce the effective volume for ensuring a capacitance because the volumes of the paste electrode layers 110 must be maintained. On the other hand, the plating layers 111 and 112 have a thickness on the order of several μm. Thus, if the external terminal electrodes 108 and 109 can be composed only of the first plating layers 111 and the second plating layers 112, the effective volume for ensuring the capacitance can be increased.
For example, Japanese Unexamined Patent Publication No. 2004-146401 discloses a method in which a conductive paste is applied to at least ridge sections of end surfaces of a component main body along the direction of laminating internal electrodes so as to come into contact with leading sections of the internal electrodes, the conductive paste is baked or thermally cured to form a conductive film, and further, the end surfaces of the component main body are subjected to electroplating, thereby forming an electroplating film so as to be connected to the conductive film on the ridge sections. According to this method, external terminal electrodes at the end surfaces can be reduced in thickness.
Furthermore, Japanese Unexamined Patent Publication No. 63-169014 discloses a method in which a conductive metal film is deposited by electroless plating on the entire sidewall surface of a component main body, at which internal electrodes are exposed, so as to short circuit the internal electrodes exposed at the sidewall surface.
However, in the methods for forming external terminal electrodes as described in Japanese Unexamined Patent Publication No. 2004-146401 and Japanese Unexamined Patent Publication No. 63-169014, plating is performed directly on the ends at which the internal electrodes are exposed. Thus, a plating solution entering the component main body along the interfaces between the internal electrodes and the insulator layers may erode the ceramic defining the insulator layers and the internal electrodes, thereby causing structural defects. Furthermore, this causes defects in terms of reliability, such as degraded load characteristics against humidity for the laminated electronic component.
In particular, when tin or gold plating is to be applied, the problems described above are more likely to occur because a tin or gold plating solution generally contains a highly corrosive complexing agent.
In order to solve the problems described above, for example, International Publication No. WO2007/119281 suggests providing a water repellent on end surfaces of a component main body at which respective ends of internal electrodes are exposed, to fill gaps at interfaces between insulator layers and the internal electrodes with this water repellent, and then forming plating layers as bases of external terminal electrodes onto the end surfaces. The application of such a water repellent can improve the lifetime characteristics in the load test against humidity.
However, the technique described in International Publication No. WO2007/119281 has the following problems.
The water repellent is likely to adhere to the ceramic sections provided from the insulator layers rather than the metal sections provided from the internal electrodes. If the distance between the internal electrodes is relatively large (that is, when the insulator layers are thick and the number of laminated internal electrodes is small), most portions of the end surfaces at which the respective ends of the internal electrodes are exposed will be covered with the water repellent, thereby decreasing the depositions plated on the end surfaces at which the internal electrodes are exposed.
Furthermore, for the purpose of enhancing the fixing strength of the external terminal electrodes to the component main body, a heat treatment may be performed at a temperature o of 800° C. or more after the formation of the plating layers as bases. However, such a heat treatment will cause the water repellent to disappear.
It is to be noted that, for example, Japanese Unexamined Patent Publication No. 2002-289465 discloses providing a water repellent before a plating process, in a case of forming paste electrode layers by baking and then performing plating as in the conventional art described with reference to FIG. 3, rather than forming external terminal electrodes substantially only by plating. The paste electrode layers formed by baking are not only formed on end surfaces of a component main body in the shape of a rectangular parallelepiped, at which the respective ends of internal electrodes are exposed, but also formed such that the end edges of the paste electrode layers are located on principal surfaces and side surfaces adjacent to the end surfaces.
However, the technique described in Japanese Unexamined Patent Publication No. 2002-289465 encounters the following problem. Moisture is likely to enter through the gap between the end edges of the paste electrode layers formed by baking and the component main body, because segregation of a glass component is likely to occur in the gaps and glass is easily dissolved by the plating solution even if the glass is coated with the water repellent.